Can there be excess height in the welds of low-temperature vessels?

Thread Content

The definition of low temperature is as follows in SH/T3525-2015, \"Welding Specifications for Low-Temperature Steels in the Petrochemical Industry\": According to relevant information, the defined temperatures for low-temperature steels are -10°C, -20°C, -29°C, and -20°C to -269°C. Japanese standards define -10℃ as a low temperature, while Germany’s DIN standards specify that the operating temperature range for low-temperature steels is between -20℃ and -269℃; some sources also cite -40℃ as a low temperature. The ASME codes in the United States do not provide a clear definition for low temperatures, but it uses -20°F (-29°C) as a control parameter, which applies equally to both vessels and pipelines. GB150 defines low-temperature pressure vessels as those with a temperature of -20°C or lower. GB50517, the Code for Acceptance of Construction Quality of Petrochemical Metal Piping Projects, specifies that low-temperature pipelines are those with a design temperature of less than -29°C; therefore, no unified definition is given in this code. When welding vessels, a temperature of -20°C or lower is considered sufficient to classify them as low-temperature vessels, while when welding pipelines, a temperature of less than -29°C is required for such classification. Regarding the weld bead height in low-temperature vessels, Section 9.1.3 of SH/T3525-2015 \"Welding Specifications for Low-Temperature Steels in Petrochemical Industries\" stipulates the following requirements: a) The weld bead height in the butt joints of low-temperature steel vessels shall not exceed 10% of the wall thickness, nor more than 3 mm; b) For pipe butt joints, when the thinner wall thickness in the joint is 6 mm or less, the weld bead height on the outer surface shall not exceed 1.5 mm; when the thinner wall thickness is greater than 6 mm, it shall not exceed 2.5 mm; c) The weld bead on the inner surface of butt joints should be level with the inner wall; d) Fillet welds should have a smooth transition, otherwise they must be polished.